Rubberized fabric and process of producing the same



Patented Feb. 16, 1932 UNITED STATES PATENT; OFFICE FREDERICK H. UNTIEDT, F CHEVY CHASE, MARYLAND No Drawing.

This invention relates to rubberized fabrics and processes of producing the same and it comprises a rubberized fabric having a coating thereon of latex rubber firmly bound is thereto by a rubber bond; it further comprises a fabric having a porous coat ng thereon composed of the product of drying a stiff, dense, foam containing latex, and it further comprises a process wherein a stiff dense foam containing rubber latex is applied to a fabric to be rubberized, the coated fabric dried, washed in water and, if desired, vulcanized.

There are many ways of rubberizing fabrics. Usually a coating composition consisting of crude rubber dissolved in a volatile solvent to form a pasty mass is applied to a fabric and pressed thereon so that by mere adhesion the rubber paste binds itself to the fabric. Thereafter the solvent is driven off 29 and the coating vulcanized. Ordinarily sulphur and additional agents such as zinc oxide, mixed in with the pasty rubber coating composition prior to application to the fabric. These processes possess disadvantages. 55 Volatile solvents are necessary and must be recovered. Their use presents a fire hazard as well. It is also difiicult, if not impossible, to secure a firm, non-peelable, union between fabric and rubber coating or a coating which 30 will not check or chip. Most rubber coatings made in this way will in time deteriorate and then be peeled off. It is of course dililcult to saturate the upper surface of the fabric with such apaste in the hope of obtaining a firm rubber bond.

Later. is an ideal material for coating fabrics in a sense because it is highly penetrative and readily saturates the individual fibres or threads of the fabric. However, latex is almost as fluid as water and readily runs through a fabric so that relatively thick coatings of latex rubber cannot be secured by a single application of latex to the fabric. It u is possible to secure a relativel thick coating of latex rubber on one side 0 a fabric by a series of coating operations, the latex being allowed to dry before additional applications are made. I

It has been su gested to overcome this disadvantage by t ickening the latex by the Application med Rovember 13, 1929. Serial No. 406,978.

addition thereto of a thickening agent. Aluminum. sulphate has, for example, been added to latex to accomplish this purpose.

I have now found that excellent coatings, possessing new characteristics, may be ob tamed upon fabrics when using the latex of commerce or other aqueous rubber dispersions provided the latex is applied to the fabric as a stiff, dense, relatively stable, foam. I spread such a foam upon the fabrics as a coating, say as much as a quarter of an inch thick and then allow the coating to dry. The dried coating is initially porous and this is advantageous in certain relations. When I wish to make a waterproof non-porous material, I simply pass the initially porous coated material between rollers or otherwise compress the coating to destroy the minute cells pherein and weld the coating into a solid aycr.

In my copending application, Serial Number 200,30d, filed June 20, 1927 now Patent 1,777,945 of which the present application is a continuation in part, have described ways of making such a foam. In its broadest aspects, the process comprises agitating and aerating latex containing soap or saponin or other foam stabilizing agent until a stiff, dense, relatively stable, foam is obtained. Such a foam contains minute bubbles hard- 1 discernible with the naked eye and is much like stiflly whipped cream. Indeed the foam looks very much like whipped cream and the operation of making it on a small scale is much the same. A properly prepared foam is relatively stable in the sense that a layer thereof will dry without much, if any breakdown of the foam to its original liquid state.

More specifically, good results can be had when the foam is made as follows. To six parts by volume of latex, I add about three parts by volume of a concentrated soap solution containing from 30 to 40 percent of soap. A soap solution of this character will jell When cool and I add it to the latex while it is at a moderately elevated temperature, just warm enough so that it is sufficiently fluid to mix well with the latex. The resulting mixture is then vi orousl agitated or beaten in such a way t at v0 umes of air will be incorporated therein. Agitators of the eggbeater type will do this. On a large scale, it is better to provide means to posit1veI introduce air into the mixture, for examp e by 5 means of pipes terminating beneath the surface of the solution.

Vi orous agitation coupled with aeration rapi 1y converts 'the solution into a stiff dense foam. The foam should be so stiff that a half a tumbler full may be inverted without displacing the foam. time required for complete conversion of the foregoing solution to the foam condltion w1ll of course depend somewhat upon the quantities and apparatus used. On a very small scale, with an ordinary e gbeater, seven minutes vigorous agitation 1s suflicient.

It shouldbe noted however that these proportions are variable and with some latices less or more soap may be required, As little as one percent soap will suffice although thelength oftime the solution must be aerated and agitated is considerably increased. It is assumed that tests will be made upon small quantities of latex prior to working up large batches so that the best ratio of soap and latex may be determined in advance. Indeed with some foam stabilizing agents, much less is required. When saponin is used not so much will be necessary. Generally speakmg, the mixture of latex and soap, prior to agitation and aeration, should have such a composition that the mixture will assume a somewhat pasty, thick condition upon standing for a few hours. Since the coated fabric is eventually subjected to a washing 0 eration to wash out the soap in the dried 0am, an excess of soap is not detrimental. 10 to 20 percent is an advatageous quantity. T00 much soap, however, should be avoided. The proportions 'ven above yield satisfactory results with t e 30 to 35 percent latex of commerce. However prepared, the foam should be of such a consistency that, when allowed to dry in sheets, not much, if any, breakdown of the foam to a liquid condition accompanied by the formation of greatly enlarged bubbles of. air, takes place. This is what mean by a relatively stable foam. If bottled so as to prevent the evaporation of water, in

time the foam will however, break down considerably yet such a foam is sufliciently stable for my purpose since it will dry-out in air to form a coating 'or sheet.

After the foam is prepared, it is then applied to the'fabric by spreading it thereon. The thickness will vary with the thickness desired in the'finished material. Generally so the coating as initially applied should be several times that eventually desired. A coating a quarter of an inch thick will give satisfactory results. I 'The dense. foam is evenly spread over the surface of the fabric by suit- .able apparatus well known in the art of coat- The precise length of partially ing fabrics and forming no part of this invention and then allowed to dry.

Ordinaril I find that good results are bad if the coate fabric is simply exposed to ordinary room temperature conditions, say F. Moderately elevated temperatures can be used but high temperatures should be avoided because they tend to break down the structure of the foam. It is of course desirable that the physical structure of the foam remain fairly constant during the drying so that not much breakdown occurs. If slight se ar ation of liquids takes place, this is an a vantage rather than the contrary because as a result the threads of the fabric become saturated with latex and thus, as the drylng continues, a firm bond is established between the coating and the underl ing threads of the fabric. If the foam e too stiff, or the quantities of stabilizin agent too great there may be less tendenc or the threads of the fabric to be saturate at least artially and the dried coating may then be ess firmly bonded to the fabric. It is of course desirable to establish a firm bonding between the coating and the fabric. Generally speaking, most relatively stable foams will wet the fabric to a suflicient degree to secure a bonding of rubber.

After the coating is practically dry, a condition easil recognized, the fabric will be covered wit a porous, absorbent, surface of latex rubber and foam stabilizing agent and the thickness thereof will not be very much less than that of the wet foam as applied.

The material thus prepared is an intermediate raw material from which finished coatings of varying characteristics can be prepared, and constitutes an important feature of my invention. It can be further rocessed to yield either a porous coated abric or a water-proof, non-porous, fabric. If the coated material is gently washed in water, as by immersion in a tank thereof or by passing through a trough, the soap or other foam stabilizer is easily washed out. After the washed, coated, fabric is allowed to dry, the coating thereon will be found to be porous. It absorbs water and, when the coated surface is wetted, the water penetrates through to the underside of the fabric.

Porous material of this sort may beput to numerous uses. For example, surgical belts are improved when the rubber portions thereof can take up moisture. The material is also an effective filter for removing finely divided dust from gases, as a separator in storage batteries, etc.

When it is desired that the coatin shall be waterproof, the intermediate drie materiel is washed as before and then subjected to pressure to destroy the porous character. This is a simple operation. Passage between rollers or other methods can be used. Alternatively the intermediate raw material can latices.

be compressed to destroy the air cells and then washed to remove the soap. This procedure seems to result in a somewhat softer finished product and is to be preferred.

The finished rubberized fabric whether the coating be porous or homogenous throughout, has a soft feel and is not so characteristicall rubbery as rubberized fabrics prepare in the ordinary way. The color is a pure white and the feel is more like a fine suede leather than rubber. Such coated fabrics are somewhat lighter in weight than ordinary fabrics and are useful in many relations, aside from those to which ordinary rubberized fabrics are put.

The finished fabric can be vulcanized by the cold processes usually used for vulcanizing latex rubber in sheet form and the vulvanization forms no part of the present invention per se. It may further be noted that fillers can be incorporated in the rubber coating by mixing such fillers with the latexfoam stabilizer mixture prior to conversion thereof into the foam condition. Some dis-.

cretion must of course be used in this connection. If the fillers inhibit foam formation in an ordinary soap solution, a foam stabilizing agent such as saponin should be chosen. Saponin is unefi'ected by electrolytes which ordinarily prevent the foaming of soap.

In the appended claims, I mean the term rubber latex to include aqueous dispersions of rubber generally, such as the synthetic By the term fabrics I mean to include tire cords and other types of woven material as well as the fabric backings usually rubberized. Tire cords can of course be coated with the dense foam to form a rubber coated cord, porous or otherwise.

Having thus described my invention, what I claim is:

1. The process of providing textile fabrics with a coating or layer of rubber which includes the steps of a plying to the fabric a layer of a dense, relatively stable aqueous foam containing a rubber latex as the rubber constituent thereof, drying the foam where by a porous rubber layer is formed, and compressing the dried layer to decrease its porosity to the desired extent.

2. The process of providing textile fabrics with a coating or layer of rubber which includes the steps of a plying to the fabric a layer of a dense, re atively stable aqueous foam containing a rubber latex as the rubber constituent thereof, drying the foam whereby a porous rubber-layer is formed, compressing the dried layer to decrease its porosity to the desired extent, and vulcanizmg the rubber.

' 3. The process as in claim 1 wherein the dried porous layer is compressed 'to an extent-r suflicient to yie d a substantially non-porous, waterproof coating on the fabric.

4. The process as in claim 2 wherein the dried porous layer is compressed to an extent suflicient to yield a substantially nonporous, waterproof coating on the fabric.

FREDERICK H. UNTIEDT. 

